Skin Integument Objectives To gain a greater appreciation of the diversity of functions of skin

To recognize the different cell types and structures of the skin which make possible this functional diversity Functions of Skin: Functional Diversity of Skin • Protects against injury and desiccation • Maintenance of water balance • Excretes/secretes various substances • • Receives stimuli − Temperature − Pain − Pressure • Basis of recognition and yields clues to one’s well being • Fat metabolism in the subcutaneous layer Fat Metabolism in the Subcutaneous Layer

Fat Metabolism in the Subcutaneous Layer

Obesity =

Too much fat in the Subcutaneous Layer

BINARY ORIGIN OF SKIN

EPIDERMIS – ECTODERM

DERMIS - MESODERM

31 Skin Overview and Introduction

• http://www.youtube.com/watch?v=yKAzVC0WcmI

Stratum Corneum

Stratum Granulosum

Stratum Spinosum

Stratum Basale Layers of the : palms and soles of feet

Stratum Corneum – Keratinized flattened, denucleated, dead cells

Stratum Granulosum – Keratohyalin granules

Stratum Spinosum – Tonofibrils – desmosomes

Stratum Basale – Continual renewal of epidermis

Stratum Basale

Stratum Spinosum

Stratum Spinosum Stratum spinosum

Slide 29: Thick Skin on finger cont.

Keratohyalin granules The epidermis of Desmosomes thick skin is Hemidesmosomes subject to continuous1

friction and Epidermis pressure so the abundant desmosomes Stratum (and tonofibrils) spinosum withstand this and hold the cell layers together. Stratum basale

Stratum Corneum Stratum Granulosum

Stratum Corneum

Stratum Corneum

Three Types of Granules in

Melanin – Skin pigment – Produced by melanocytes and passed by cytocrine secretion to keratinocytes

Membrane coating granules (lamellated granules) – Water proofing function – Produced by keratinocytes

Keratinohyalin granules Three Types of Granules in Keratinocytes

Keratinohyalin granules

– Chemical nature not clearly established

– Rich in histodine forms

– Matrix of cells in stratum corneum, stability due to disulfide bonds

– Absent in and nails Sun from Slide 31: Thin Skin (scalp) NASA

Stratum corneum

Stratum granulosum

Stratum spinosum

4 Melanin capping Stratum basale of nuclei Capping of Melanin Granules in Keratinocytes in Stratum Basale

Capping

105 Melanin is produced by Melanocytes

Melanin-producing enzymes in Melanocytes

Space of removed dermis

Epidermis Regional Variation of the Epidermis

Thick skin - sole of foot (1.4 mm thick)

Thin skin - and most of body (0.07 to 0.12 mm)

Cornea of eye - transparent

Appendages - hair follicles, nails, glands Regional Variation of the Epidermis

Cells in Epidermis

Stratified squamous - cell types include:

• Keratinocytes - main cell = Renewal of skin by cell type – ectoderm division and differentiation • Melanocytes - pigmentation - neural crest • Langerhans cell - immunologic role • Merkel cells - associated with endings CYTOCRINE SECRETION - PASS MELANIN GRANULES FROM MELANOCYTES TO KERATINOCYTES Clinical Correlation

Albinism can be caused by a hereditary defect in tyrosinase activity or the inability of cells to

take up tyrosine. Tyrosine amino acid figure chemistry.about.com.

Patient with albinism would be more at risk for the development of basal and squamous cell carcinomas as albinism produces skin hypopigmentation so fewer melanin granules to protect nuclear DNA from the ionizing, mutagenic effects of UV radiation. Albino peacock http://www.duskyswondersite.com/animals/albino-animals/

Melanocyte - pigment synthesis

Freckles - melanin distributed in patches

Melanocyte - pigment synthesis

Freeze branding in cattle Melanocyte stimulating hormone secreted by the pars intermedia Melanocyte – disease states

Albinism - failure to produce melanin

Malignant melanomas - cancer

Addison’s disease - pigment deposition in skin due to adrenocortical insufficiency Langerhans cells

Bone marrow origin Located in stratum spinosum - gold chloride stain

Clear cell - no desmosomes Dendritic cell

Langerhans cells

Dendritic cell Rod or racket shaped granules

Function - immunologic role as an antigen- presenting cell

Contact allergic responses and other cell mediated reaction of the skin Epidermal – dermal interface

Epidermal – dermal interface Epidermis

Rete pegs of epidermis

Dermal papillae

Dermis Epidermal – dermal interface

Epidermal – dermal interface

Epidermal – dermal interface

Epidermis pulled off of dermis dermal view of epidermis Epidermal – dermal interface - finger pad PAPILLARY LAYER Dermis

Two layers”

Papillary layer - sculptured layer of dermis Reticular layer - deeper main portion of dermis, rather dense irregular CT

Melanin-producing enzymes in Melanocytes

Dermal papilla removed

Rete pegs of epidermis Dermis Elastic fibers - Network between collagen bundles muscle

Smooth muscle - loose plexus in reticular layer in areolae, penis, , and scrotum Epidermis

Smooth muscle

Dermis Muscle - terminated in the dermis • Facial expression

Dermis Muscle Skeletal muscle - terminated in the dermis • Facial expression

Cutaneous appendages

Hair – Follicles – Pigmentation – Graying

108 Hair Graying with age

Every contains pigment cells called melanocytes. The melanocytes produce eumelanin, which is black or dark brown, and pheomelanin, which is reddish-yellow, and pass the melanin to the cells which produce , the chief in hair. When the keratin-producing cells (keratinocytes) die, they retain the coloring from the melanin. When you first start to go gray, the melanocytes are still present, but they become less active. Less pigment is deposited into the hair so it appears lighter. As graying progresses, the melanocytes die off until there aren't any cells left to produce the color.

Http://chemistry.About.Com/od/howthingsworkfaqs/f/why -does-hair-turn-gray.Htm

Regeneration of epidermis

Glands of epidermal origin

Sweat glands – Eccrine: common - local cooling

– axillary region: function in animals Sweat Gland Secretions

Human Skin, Mode of secretion of the scalp 108 sebaceous glands is holocrine where by the sebum is Skin, released when cells burst. scalp

sebaceous glands Eccrine sweat glands Sweat Glands Slide 29: Thick Skin (ventral surface of finger)

Myoepithelial cells are eosinophilic because of the presence of muscle contractile , which contract to expel sweat when needed.

Ducts of eccrine sweat glands with Myoepithelial cells Eccrine sweat glands stratified cuboidal epithelium Slide 66: Recto-anal junction

skin

Anal opening

Sebaceous gland Hair follicle Apocrine sweat gland Slide 66: Recto-anal junction

hair

Sebaceous gland Apocrine sweat gland Other Glands of Epidermal Origin

Cerumenous glands - produce wax (cerumen) in the ear for waterproofing and discourage entry of insects

Tarsal lacrimal glands - tears of the eye

Other Glands of Epidermal Origin

Cerumenous glands - produce wax (cerumen) in the ear for waterproofing and discourage entry of insects

Tarsal lacrimal glands - tears of the eye

Tarsal gland of meibomian – wax-like secretion that holds in tears Other Glands of Epidermal Origin – Other Glands of Epidermal Origin – Mammary Gland Gland for which our class, mammalia, was named. Mammals are characterized by hair on skin, special ear bones, and -producing mammary glands in females for nourishment of young. Variations in the Microvasculature Common Arteriole  Capillary  Venule

Shunts Arteriole  Metarteriole  Venule

arteries  av shunt  venules

Circulation of Blood Through Skin: Blushing? Circulation of Blood Through Skin

Function and structure Nutrition - capillaries Heat conduction from body Subcutaneous venous plexus (holds large quantities of blood to heat skin) Arterio-venous anastomoses Circulation of Blood Through Skin Circulation of Blood Through Skin

Blood volume capacity of skin is 4.5% of total blood volume

Circulation of Blood Through Skin

Blood flow through skin in an average adult – Normal conditions - 400 mL/min. – Hot conditions - 2.8 liters/min

(Volume 5-6 L = 12-13 pints/person)

Circulation of Blood Through Skin

Blood vessels in different layers Of skin to accommodate variation in flow rate. 109 Skin hand monkey

Eccrine sweat glands Adipocytes Hypodermis

Pacinian corpuscles

Dermal Epidermal peg papillae Papillary layer Epidermal and dermal – nerve interfaces The End bulb of Krause is a thermoreceptor that picks up on the sensation of cold temperatures.

Pain receptors are found on free nerve endings located in many tissues throughout the body. This includes skin, muscles, joints, connective tissues, and internal organs. Pain receptors are activated in response to a painful stimulus, usually involving tissue damage. Epidermal and dermal– nerve interfaces

Merkel cells or Merkel-Ranvier cells are oval receptor cells found in the skin of vertebrates that have synaptic contacts with somatosensory afferents. They are associated with the sense of light touch discrimination of shapes and textures. Genetic knockout mice have recently shown that Merkel cells are essential for the specialized coding by which afferent resolve fine spatial details. Meissner's corpuscles (or tactile corpuscles) are a type of nerve ending in the skin that is responsible for sensitivity to light touch. In particular, they have highest sensitivity (lowest threshold) when sensing vibrations lower than 50 Hertz. They are rapidly adaptive receptors. Any physical deformation in the corpuscle will cause an action potential in the nerve. Since they are rapidly adapting or phasic, the action potentials generated quickly decrease and eventually cease (this is the reason one stops "feeling" one's clothes).

Epidermal and dermal – nerve interfaces Meissner's Corpuscles (or tactile corpuscles) • The number of Meissner’s corpuscles per square millimeter of skin on the fingertips drops four fold between the ages of 12 and 50. The rate at which they are lost correlates well with the age-related loss in touch sensitivity for small probes (Thornbury and Mistretta, Histo 029 1981). Epidermal and Dermal – Nerve Interfaces

A Pacinian corpuscle is a type of touch receptor located in the skin. It is classed as a mechanoreceptor, meaning it is part of the group of sensory receptors that respond to touch and pressure. 105 Pacinian corpuscles are especially suited to feeling rough surfaces and detecting vibration. They respond to transient touches rather than sustained pressure. This is because a Pacinian corpuscle is able to quickly adapt to pressure so that it no longer acts as a stimulus. Epidermal and Dermal – nerve Interfaces Mucocutaneous Junctions

Lips, Nares, , or Prepuce Anal Canal

Functional Diversity of Skin

• Protects against injury and desiccation • Maintenance of water balance • Excretes/secretes various substances • Thermoregulation • Receives stimuli − Temperature − Pain − Pressure • Basis of recognition and yields clues to one’s well being • Fat metabolism in the subcutaneous layer